Checkerboard buffer using sequential memory locations

ABSTRACT

Methods and apparatus for storing and retrieving data in parallel but in different orders. In one implementation, data for pixels is stored according to a checkerboard pattern, alternately between two memory devices, forming a checkerboard buffer. In one implementation, a checkerboard buffer includes: a data source, providing data in a first order; a data destination, receiving data in a second order; at least two memory devices, each memory device having a plurality of memory locations, where data is stored in parallel to the memory devices and retrieved in parallel from the memory devices, and where data is stored according to the first order using sequential memory locations in the memory devices; a first data switch connected to the data source and each of the memory devices, where the first data switch controls which data is stored to which memory device; and a second data switch connected to the data destination and each of the memory devices, where the second data switch controls providing data to the data destination according to the second order.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/269,784 filed Feb. 15, 2001, and of U.S. Provisional Application No.60/269,783 filed Feb. 15, 2001, the disclosures of which areincorporated herein by reference.

This application is related to the following co-pending and commonlyassigned patent applications: application No. 09/908,295 filed on Jul.17, 2001, application No. 09/907,854 filed on Jul. 17, 2001, applicationNo. 09/908,301 filed on Jul. 17, 2001, the disclosures of which areincorporated herein by reference.

BACKGROUND

The present invention is related to video data storage. Moreparticularly, the present invention is related to video display systemsand frame buffers. Several related technologies are discussed below (inlabeled sections for clarity).

1. Raster-Scan Displays

A common type of graphics monitor is a conventional raster-scan displayusing a cathode ray tube (“CRT”). As is well known, in a typical CRT, anelectron beam strikes phosphor on the inner surface of the screenproducing light visible on the outer surface of the screen. Bycontrolling the electron beam different locations of the screen can bestruck, creating a pattern and hence a video image. In a typical CRTraster-scan display, the screen area is divided into a grid of pixels(or picture elements). The electron beam sweeps from left to rightacross the screen, one row at a time from top to bottom, progressivelydrawing each pixel on the screen. Each row of pixels is commonlyreferred to as a scan line. In this type of conventional display, thescan lines are horizontal. The number of pixels in a single scan line isreferred to as the width. One complete pass over the screen and thepixels in that pass are commonly referred to as a frame. As the electronbeam moves across the pixels of each scan line, the beam intensity canbe adjusted to vary the light produced by the screen phosphorcorresponding to the pixels. The light emitted by the phosphor of thepixels creates a pattern of illuminated spots forming the video image.The intensity of the electron beam is controlled by image data stored ina section of memory called the frame buffer or refresh buffer.

2. Grating Light Valves

Another type of display system uses one or more grating light valves(“GLV”) to produce an image. GLV's are known devices, and a descriptioncan be found in (among other sources) a paper by D. M. Bloom of SiliconLight Machines, Inc., titled “The Grating Light Valve: revolutionizingdisplay technology” (1997; available from Silicon Light Machines; and acopy of which has been filed in an Information Disclosure Statement forthis application), and in an article (and therein cited references) byR. W. Corrigan and others of Silicon Light Machines, Inc., titled “AnAlternative Architecture for High Performance Display” (presented at the141^(st) SMPTE Technical Conference and Exhibition, Nov. 20, 1999, inNew York, N.Y.), the disclosures of which are incorporated herein byreference. In overview, a GLV uses a combination of reflection anddiffraction of light to create an image. A GLV includes aone-dimensional array of GLV pixels, each GLV pixel including a numberof microscopic “ribbons.” The ribbons for each GLV pixel can bedeflected through electrostatic force to create an adjustablediffraction grating. In a non-deflected state, the ribbons reflectlight. As the ribbons are deflected, the ribbons increasingly diffractlight. Accordingly, by controlling the ribbons, the proportion of lightthat is either reflected or diffracted can be controlled for each GLVpixel. The GLV deflects the ribbons for each GLV pixel according toimage data, such as pixel data received from a frame buffer.

An array of GLV pixels can create a column of visible pixels, such as1088 pixels, typically an entire column at a time. A GLV can be used tocreate a vertical column of pixels in a high definition resolutionimage, such as a screen resolution of 1920 pixels horizontally by 1080pixels vertically (with some of the 1088 pixels left blank or dark). Byproviding a GLV with pixel data representing columns of pixels in aframe, the GLV can create the frame of pixels, one column at a time,sweeping from left to right. The location of each column of pixels canbe controlled external to the GLV array, such as through lenses and anadjustable mirror, rather than moving the GLV itself. A combination ofthree GLV's for red, green, and blue can be used to produce a colorimage.

3. Frame Buffers

FIG. 1A is a representation of a screen 105 as a grid of pixels 110. InFIG. 1A, for simplicity, screen 105 is only 4×4 nd so only 16 pixels areshown, but a typical screen has many more pixels. One common screenresolution is high definition (“HD”) resolution, where screen resolutionindicates the number of pixels in a frame and is typically given as thehorizontal resolution (number of pixels in one row) versus the verticalresolution (number of pixels in one column). HD resolution is either1920×1080 (2,073,600 total pixels per frame) or 1280×720 (921,600 pixelsper frame). Herein, HD resolution refers to 1920×1080.

Returning to FIG. 1A, the pixels 110 are often numbered sequentially forreference. Pixel 0 is typically at the upper left. FIG. 1B is arepresentation of a memory device 150 implementing a frame buffer as agrid of memory locations 155. Typical memory devices include SDRAM(synchronous dynamic random access memory). The actual memory deviceused may vary in different devices, but the memory locations for theframe buffer are typically in a contiguous block of locations withsequential addresses. Memory device 150 has a memory location 155 forstoring pixel data (e.g., an intensity value) for each pixel 110 ofscreen 105. In some implementations, pixel data for more than one pixelis stored at each memory location. In many conventional raster-scansystems, pixel data is stored in memory locations adjacent to oneanother in the same pattern as the pixels on the screen. In FIG. 1B,each memory location 155 is numbered with the number of the pixel (110from FIG. 1A) corresponding to the pixel data stored in that memorylocation 155. For example, the pixel at the upper left of the screen ispixel 0 in FIG. 1A and pixel data for pixel 0 is stored in the firstmemory location in memory device 150, as indicated by the “0” in theupper left memory location 155. The second memory location stores pixeldata for pixel 1, the fifth memory location stores pixel data for pixel4, and so on.

4. Pixel Rates

FIG. 2 is a representation of screen resolutions and typical datathroughput requirements. FIG. 2 shows four resolutions in respectiveareas: VGA resolution (640×480) 205, XGA resolution (1024×768) 210, SXGAresolution (1280×1024) 215, and HD resolution (1920×1080) 220. The pixelrate for a screen resolution is the number of pixels per second thatneed to be processed to maintain the screen resolution at a specifiedrefresh rate (i.e., the number of times a complete frame is drawn to thescreen per second). While pixel rates vary among implementations, thepixel rates shown in FIG. 2 are representative. These pixel rates aregiven in megapixels per second (“MP/S”). For example, according to SMPTE274M-1998 (a specification defining, among other things, pixel rates forresolutions of 1920×1080), for HD resolution 220 the pixel rate is about150 MP/S @ 60 Hz. FIG. 2 also shows a corresponding approximate datarate in megabytes per second (“MB/S”) for each resolution. The data rateis the number of bytes per second to be processed based on the number ofbytes per pixel and the pixel rate. For example, HD resolution 220 has adata rate of 450 MB/S, at 24 bits per pixel (3 bytes). If each pixel has32 bits of data, the data rate for HD resolution is 600 MB/S. However,the data rate of a typical 32-bit wide SDRAM running at 125 MHZ isapproximately 500 MB/S. A frame buffer architecture using two 125 MHZSDRAM's can realize a data rate of approximately 1000 MB/S.

5. Frame Buffers Using Parallel Storage in Two Memory Devices

FIG. 3A is a representation of a frame 305 of pixels 310 divided betweentwo memory devices. Frame 305 has only 32 pixels for simplicity, but, asnoted above, a typical HD resolution frame has 2,073,600 pixels. FIG. 3Bis a representation of a first memory device 350 and FIG. 3C is arepresentation of a second memory device 375. Each pixel 310 in frame305 is numbered, starting with pixel 0 in the upper left of frame 305.Even-numbered pixels are stored in first memory device 350 andodd-numbered pixels are stored in second memory device 375. The pixelsstored in second memory device 375 are also shaded for clarity in FIGS.3A and 3C.

FIG. 4 is a block diagram of a typical frame buffer architecture 400capable of accessing pixel data for two pixels in parallel, supportingthe representations shown in FIGS. 3A, 3B, and 3C. A video source 405provides pixel data to a first memory 410 (recall first memory device350 in FIG. 3B) and to a second memory 415 (recall second memory device375 in FIG. 3C) in parallel and a video destination 420 retrieves pixeldata from first memory 410 and from second memory 415 in parallel. Inthis implementation, pixel data for each pixel is stored in a separateaddressable memory location. Video source 405 receives video data fromanother source (not shown), such as a broadcast source or a softwareapplication running on a computer system connected to video source 405.Video destination 420 controls the display of each pixel on a videodevice (not shown), such as a CRT. First memory 410 and second memory415 are separate memory devices such as two SDRAM's. A first data bus425 is connected to video source 405, first memory 410, and videodestination 420. A second data bus 430 is connected to video source 405,second memory 415, and video destination 420. A source address bus 435is connected to video source 405 and a first input 440 of an addressmultiplexor 445. A destination address bus 450 is connected to videodestination 420 and a second input 455 of address multiplexor 445. Anoutput 460 of address multiplexor 445 is connected to first memory 410and second memory 415. Accordingly, the same address is provided to bothfirst memory 410 and second memory 415. Address multiplexor 445 receivesa control signal (not shown) to cause first input 440 or second input455 to connect to output 460. First memory 410 and second memory 415also receive control signals (not shown) to control whether memories 410and 415 will read in data (write mode) or read out data (read mode). Inaddition, while clock lines are not shown in FIG. 4, architecture 400operates based on clock cycles so that pixel data can be processed fortwo pixels per clock cycle in support of the desired pixel rate.

In operation, memories 410 and 415 read in or store complementary halvesof a frame of pixels as pixel data from video source 405 and output thepixel data to video destination 420. To store pixel data, memories 410and 415 are put in write mode and address multiplexor 445 is set toconnect first input 440 to output 460. Video source 405 provides pixeldata for a first pixel to first data bus 425, such as pixel 0 in FIG.3A, and pixel data for a second pixel to second data bus 430, such aspixel 1 in FIG. 3A. First data bus 425 provides its pixel data to firstmemory 410 and second data bus 430 provides its pixel data to secondmemory 415. Video source 405 also provides an address to source addressbus 435. To calculate the address, video source 405 can use a counter.Because each memory 410 and 415 stores pixel data for half the pixels inone frame, the counter typically ranges from 0 to one less than one-halfof the number of pixels in one frame. Video source 405 can increment thecounter by 1 for each pixel pair. Source address bus 435 provides theaddress to first input 440 of address multiplexor 445. Addressmultiplexor 445 in turn provides the address to first memory 410 andsecond memory 415. First memory 410 stores the pixel data on first databus 425 at the address supplied by address multiplexor 445 from videosource 405. Second memory 415 stores the pixel data on second data bus430 at the same address. Two pixels have been stored in parallel in twomemories using the same address. Referring to FIGS. 3A, 3B, and 3C,pixel 0 and pixel 1 are stored at the same time at the same address infirst memory device 350 and second memory device 375, respectively.Accordingly, for example, pixel 0 is at address 0 in first memory device350, pixel 1 is at address 0 in second memory device 375, pixel 2 is ataddress 1 in first memory device 350, pixel 3 is at address 1 in secondmemory device 375, and so on.

To retrieve pixel data, memories 410 and 415 are put in read mode andaddress multiplexor 445 is set to connect second input 455 to output460. Video destination 420 provides an address to destination addressbus 450. Destination address bus 450 provides the address to secondinput 455 of address multiplexor 445. Address multiplexor 445 in turnprovides the address to first memory 410 and second memory 415. Firstmemory 410 provides the pixel data stored at the address supplied byaddress multiplexor 445 from video destination 415 to first data bus425. Second memory 415 provides the pixel data stored at the sameaddress to second data bus 430. First data bus 425 provides its pixeldata to video destination 420 and second data bus 430 provides its pixeldata to video destination 420. Two pixels have been retrieved inparallel from two memories using the same address. Referring to FIGS.3A, 3B, and 3C, pixel 0 and pixel 1 can be retrieved at the same timeusing the same address from first memory device 350 and second memorydevice 375, respectively.

FIG. 5 is a block diagram of another implementation of a dual pixelframe buffer architecture 500. Architecture 500 is similar toarchitecture 400 of FIG. 4, but a memory controller 545 provides dataand addresses to memories 510 and 515. Memory controller 545 receivespixel data from video source 505 to store in memories 510 and 515.Memory controller 545 retrieves pixel data from memories 510 and 515 andprovides the pixel data to video destination 520. Memory controller 545replaces address multiplexor 445. Memory controller 545 receives signalsfrom video source 505 and video destination 520 indicating whether pixeldata is to be stored to or retrieved from memories 510 and 515. Memorycontroller 545 generates addresses and supplies these addresses alongwith control signals to memories 510 and 515. Accordingly, memorycontroller 545 controls address generation rather than video source 505and video destination 520, as compared with architecture 400 of FIG. 4.In addition, as noted above with respect to FIG. 4, architecture 500operates based on clock cycles so that pixel data can be processed fortwo pixels per clock cycle in support of the desired pixel rate.

6. Double-Buffering

Typical frame buffer architectures often also utilize“double-buffering.” Double-buffering is a well known technique where thememory address space of a frame buffer is divided into two sections. Insome architectures, each section is a separate memory device, and inother architectures one or more devices are each divided into sections.Data from a frame is stored in one section while data from a previouslystored frame is read from the other section. Series of reading andwriting operations alternate. For example, after storing pixel data for16 pixels, pixel data for 16 pixels is retrieved. After storing a frame,the sections switch roles. Pixel data for blocks of pixels can betemporarily stored before being sent to memory or after being receivedfrom memory in a buffer, such as a FIFO buffer. In architectures 400 and500 from FIGS. 4 and 5, respectively, FIFO buffers can be included inboth the video source and the video destination, or in the memorycontroller.

SUMMARY

The present invention provides methods and apparatus for storing andretrieving data in parallel but in different orders. In oneimplementation, data for pixels is stored according to a checkerboardpattern, alternately between two memory devices, forming a checkerboardbuffer. In one implementation, a checkerboard buffer includes: a datasource, providing data in a first order; a data destination, receivingdata in a second order; at least two memory devices, each memory devicehaving a plurality of memory locations, where data is stored in parallelto the memory devices and retrieved in parallel from the memory devices,and where data is stored according to the first order using sequentialmemory locations in the memory devices; a first data switch connected tothe data source and each of the memory devices, where the first dataswitch controls which data is stored to which memory device; and asecond data switch connected to the data destination and each of thememory devices, where the second data switch controls providing data tothe data destination according to the second order.

In another implementation, a checkerboard buffer includes: a videosource providing pixel data for pixels in a frame; a video destination;a first memory; a second memory; a first data bus connected to the firstmemory; a second data bus connected to the second memory; a firstaddress multiplexor connected to the first memory; a second addressmultiplexor connected to the second memory; a source address busconnected to the video source, the first address multiplexor, and thesecond address multiplexor; a first destination address bus connected tothe video destination and the first address multiplexor; a seconddestination address bus connected to the video destination and thesecond address multiplexor; a first data switch connected to the firstdata bus, the second data bus, and the video source, where the firstdata switch is between the video source and the first memory and betweenthe video source and the second memory, and where the first data switchswitches which memory to store pixel data for two pixels with eachhorizontal row of pixels; and a second data switch connected to thefirst data bus, the second data bus, and the video destination, wherethe second data switch is between the video destination and the firstmemory and between the video destination and the second memory, andwhere the second data switch switches the order pixel data from each ofthe first memory and the second memory is provided to the videodestination with each vertical column of pixels; where pixel data isstored in the first memory and the second memory according to horizontalrows of pixels in the frame, and pixel data is stored in sequentialmemory locations in the memory devices.

In another implementation, a method of storing pixel data in acheckerboard buffer includes: storing pixel data for a first pair ofpixels at a first memory address in a first memory device and a secondmemory device respectively, where the first pair of pixels are the firsttwo pixels in a first horizontal row of pixels in a frame; and storingpixel data for a second pair of pixels at a second memory address in thesecond memory device and the first memory device respectively, where thesecond pair of pixels are the first two pixels in a second horizontalrow of pixels in a frame and are vertically adjacent to the first pairof pixels; where pixel data is stored in sequential memory locations inthe memory devices.

In another implementation, a method of retrieving pixel data from acheckerboard buffer includes: retrieving pixel data for a first pair ofpixels from a first memory address in a first memory device and from asecond memory address in a second memory device respectively, where thefirst pair of pixels are the first two pixels in a first vertical columnof pixels in a frame; and retrieving pixel data for a second pair ofpixels from the first memory address in the second memory device andfrom the second memory address in the first memory device respectively,where the second pair of pixels are the first two pixels in a secondvertical column of pixels in a frame and are horizontally adjacent tothe first pair of pixels; where pixel data is stored in sequentialmemory locations in the memory devices.

In another implementation, a method of storing and retrieving pixel datain a checkerboard buffer includes: storing pixel data for a first pixeland a second pixel at a first memory address in a first memory deviceand a second memory device respectively, where the first pixel and thesecond pixel are the first two pixels in a first horizontal row ofpixels in a frame; storing pixel data for a third pixel and a fourthpixel at a second memory address in the second memory device and thefirst memory device respectively, where the third pixel and the fourthpixel are the first two pixels in a second horizontal row of pixels in aframe, and the third pixel and the fourth pixel are vertically adjacentto the first pixel and the second pixel, respectively; retrieving pixeldata for the first pixel and the third pixel from the first memoryaddress in the first memory device and from the second memory address inthe second memory device respectively, where the first pixel and thethird pixel are the first two pixels in a first vertical column ofpixels in a frame; and retrieving pixel data for the second pixel andthe fourth pixel from the first memory address in the second memorydevice and from the second memory address in the first memory devicerespectively, where the second pixel and the fourth pixel are the firsttwo pixels in a second vertical column of pixels in a frame and thesecond pixel and the fourth pixel are horizontally adjacent to the firstpixel and the third pixel, respectively; where pixel data is stored insequential memory locations in the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a representation of a screen as a grid of pixels.

FIG. 1B is a representation of a frame buffer as a grid of memorylocations.

FIG. 2 is a representation of screen resolutions and typical datathroughput requirements.

FIG. 3A is a representation of a frame of pixels divided between twomemory devices.

FIG. 3B is a representation of a first memory device.

FIG. 3C is a representation of a second memory device.

FIG. 4 is a block diagram of a dual pixel frame buffer architecturesupporting the representations shown in FIGS. 3A, 3B, and 3C.

FIG. 5 is a block diagram of a dual pixel frame buffer architectureincluding a memory controller.

FIG. 6A is a representation of a frame of pixels divided between twomemory devices according to the present invention.

FIG. 6B is a representation of a first memory device according to thepresent invention.

FIG. 6C is a representation of a second memory device according to thepresent invention.

FIG. 7 is a block diagram of a data system according to the presentinvention.

FIG. 8 is a block diagram of a switching dual pixel frame bufferarchitecture according to the present invention.

FIG. 9 is a table of addresses and pixel numbers for storing a 1920×1080frame of pixel data according to the present invention.

FIG. 10 is a representation of address bits in a counter according tothe present invention.

FIG. 11 is a flowchart of generating addresses for storing pixel datafor a frame of pixels according to the present invention.

FIG. 12 is a flowchart of storing pixel data according to the presentinvention.

FIG. 13 is a representation of generating destination addressesaccording to the present invention.

FIG. 14 is a flowchart of generating addresses for retrieving pixel dataaccording to the present invention.

FIG. 15 is a flowchart of retrieving pixel data according to the presentinvention.

FIG. 16 is a table of addresses and pixel numbers for storing a1920×1080 frame of pixel data according to the present invention.

FIG. 17 is a flowchart of reading and writing blocks of pixels usingmemory sections according to the present invention.

FIG. 18 is a block diagram of an implementation of a switching dualpixel frame buffer architecture having a memory controller according tothe present invention.

FIG. 19 is a block diagram of another implementation of a switching dualpixel frame buffer architecture having a memory controller according tothe present invention.

FIG. 20 is a block diagram of a switching dual pixel frame bufferarchitecture having four memory devices according to the presentinvention.

FIG. 21 is a flowchart of storing and retrieving pixel data in parallelaccording to the present invention.

FIG. 22 is a block diagram of one implementation of a switching dualpixel frame buffer architecture having four memory devices and a memorycontroller according to the present invention.

FIG. 23 is a block diagram of another implementation of a switching dualpixel frame buffer architecture having four memory devices and a memorycontroller according to the present invention.

DETAILED DESCRIPTION

The present invention provides methods and apparatus for storing andretrieving data in parallel but in different orders. This descriptionfocuses on implementations where the data is pixel data, however, thepresent invention is applicable to various types of data that can beaccessed in two different orders. As described below, in oneimplementation, pixels are stored according to a checkerboard pattern,alternately between two memory devices. This pattern advantageouslyallows pixels to be stored in parallel following a horizontal row ofpixels and retrieved in parallel following a vertical column of pixels.

The description below is generally divided into two sections forclarity: A. Checkerboard Buffers; and B. Illustrative Implementations ofCheckerboard Buffers.

A. Checkerboard Buffers

A checkerboard buffer provides storage of data in one order andretrieval of data in another order. A checkerboard buffer includes twoor more memory devices for parallel storage and retrieval of data. Fortwo memory devices, half of the data is stored in each of the memorydevices. As data elements are received, which data is stored to whichmemory device changes according to the difference between the order datais received and the order data is to be retrieved. The data is stored inthe memory devices so that data can be stored to the two devices in oneorder in parallel and retrieved from the two devices in another order inparallel.

In implementations using video data, the checkerboard buffer is a framebuffer for storing pixel data. Pixel data is supplied to thecheckerboard buffer according to the horizontal order of pixels in aframe, such as from left to right, top to bottom. Pixel data isretrieved from the checkerboard buffer according to the vertical orderof pixels in a frame, such as from top to bottom, left to right. Pixeldata is stored and retrieved for a pair of pixels at a time. Pixel datafor one pixel is stored in or retrieved from one memory device and pixeldata for the other pixel in or from another memory device.

FIGS. 6A, 6B, and 6C illustrate a checkerboard pattern of storage in twomemory devices providing parallel storage and parallel retrieval. FIG.6A is a representation of a frame 605 of pixels 610 divided between twomemory devices. FIG. 6B is a representation of a first memory device 650and FIG. 6C is a representation of a second memory device 675. Frame 605has only 32 pixels for simplicity, but typical video frames have manymore pixels. For example, one HD resolution has 2,073,600 pixels perframe (1080 horizontal rows with 1920 pixels per row). The descriptionherein of checkerboard buffers focuses on this HD resolution, however,checkerboard buffers can be implemented for various resolutions (e.g.,1280×720, 640×480, etc.).

Each pixel 610 in frame 605 is numbered, starting with pixel 0 in theupper left of frame 605. Each horizontal row is numbered, with theuppermost horizontal row (i.e., pixels 0 . . . 7) numbered 0. Eachvertical column is numbered, with the leftmost column (i.e., pixels 0,8, 16, 24) numbered 0. In FIG. 6A, half of the pixels 610 are shaded(e.g., pixels 1 and 8 are shaded; “shaded” here does not refer to theappearance of pixels when displayed, but only to the representation inthe figures of this disclosure). Pixel data for unshaded pixels isstored in first memory device 650 and pixel data for shaded pixels isstored in second memory device 675. The boxes in FIG. 6B and FIG. 6C arealso shaded and unshaded to correspond with FIG. 6A.

Each box of memory devices 650 and 675 represents a memory location.Each memory location stores pixel data for one pixel and is numberedaccording to the pixel that has pixel data stored in that memorylocation. Accordingly, pixel data is stored in memory devices 650 and675 in the patterns shown in FIGS. 6B and 6C. Even-numbered pixels ineven-numbered horizontal rows are stored in first memory device 650.Even-numbered pixels in odd-numbered horizontal rows are stored insecond memory device 675. Odd-numbered pixels in even-numberedhorizontal rows are stored in second memory device 675. Odd-numberedpixels in odd-numbered horizontal rows are stored in first memory device650. Each memory location has an address. The upper left box representsthe memory location having address 0, and addresses continuesequentially from left to right, top to bottom. For example, in FIG. 6B,pixel data for pixel 0 is stored at address 0 in memory device 650,pixel data for pixel 2 is stored at address 1, pixel data for pixel 9 isat address 4, and so on. One address can be used to access two memorylocations by supplying the address to two memory devices, accessing onememory location in each memory device. For example, by supplying address0 to memory devices 650 and 675, pixel data stored in the first memorylocation of each memory device can be retrieved (i.e., pixel data forpixels 0 and 1).

Pixel data for frame 605 would be supplied to the checkerboard buffer inhorizontal pixel pairs (i.e., two pixels at a time, one for each memorydevice) according to the horizontal rows of frame 605. For example, thecheckerboard buffer would receive pixel data for pixels in frame 605according to this sequence of pixel pairs: 0-1, 2-3, 4-5, 6-7, 8-9,10-11, 12-13, 14-15, 16-17, 18-19, 20-21, 22-23, 24-25, 26-27, 28-29,30-31. The checkerboard buffer stores the pixel data using thissequence, for two pixels at a time, but changes which memory devicereceives which pixel data with each row. First memory device 650receives and stores pixel data for the first pixel in the pixel pair ineven-numbered rows and pixel data for the second pixel in the pixel pairin odd-numbered rows. Second memory device 675 receives and stores pixeldata for the second pixel in the pixel pair in even-numbered rows andpixel data for the first pixel in the pixel pair in odd-numbered rows.For example, for the first row of pixels, first memory device 650receives and stores pixel data for pixels 0, 2, 4, and 6, and secondmemory device receives and stores pixel data for pixels 1, 3, 5, and 7.For the second row of pixels, first memory device 650 receives andstores pixel data for pixels 9, 11, 13, and 15, and second memory devicereceives and stores pixel data for pixels 8, 10, 12, and 14. Thispattern continues for the rest of frame 605. Accordingly, pixel data forthe 32 pixels of frame 605 is stored in 16 locations in two memorydevices (650 and 675) in 16 parallel operations using horizontal rows.

Pixel data would be retrieved for frame 605 from the checkerboard bufferin vertical pixel pairs (i.e., two pixels at a time, one for each memorydevice) according to the vertical columns of frame 605. For example, thecheckerboard buffer would supply pixel data for pixels in frame 605according to this sequence of pixel pairs: 0-8, 16-24, 1-9, 17-25, 2-10,18-26, 3-11, 19-27, 4-12, 20-28, 5-13, 21-29, 6-14, 22-30, 7-15, 23-31.The checkerboard buffer retrieves pixel data using this sequence, fortwo pixels at a time, but changes which memory device to access forwhich pixel data with each column. First memory device 650 is accessedand provides pixel data for the first pixel in the pixel pair ineven-numbered columns and pixel data for the second pixel in the pixelpair in odd-numbered columns. Second memory device 675 is accessed andprovides pixel data for the second pixel in the pixel pair ineven-numbered columns and pixel data for the first pixel in the pixelpair in odd-numbered columns. For example, for the first column ofpixels, first memory device 650 provides pixel data for pixels 0 and 16,and second memory device provides pixel data for pixels 8 and 24. Forthe second column of pixels, first memory device 650 provides pixel datafor pixels 9 and 25, and second memory device provides pixel data forpixels 1 and 17. This pattern continues for the rest of frame 605.Accordingly, pixel data for the 32 pixels of frame 605 can be retrievedin 16 parallel operations using vertical columns.

By comparison, in the storage pattern shown in FIGS. 3A, 3B, and 3C,while pixels 0 and 1 can be retrieved in parallel from different memorydevices, pixels 0 and 8 cannot. Pixels 0 and 8 are both stored in thesame device, first memory device 350 in FIG. 3B. The checkerboard bufferallows parallel storage for horizontal rows of pixels and parallelretrieval for vertical columns of pixels because the pixel data for eachhorizontal row of pixels is divided between two memory devices and thepixel data for each vertical column of pixel is also divided between twomemory devices.

FIG. 7 is a block diagram of a data system 700. A data source 705provides data to a checkerboard buffer system 710 in a first order.Checkerboard buffer system 710 stores the data in a checkerboardpattern, as described above. Checkerboard buffer system 710 retrievesthe data in a second order and provides the retrieved data to a datadestination 715.

Data source 705 can be a video source providing pixel data tocheckerboard buffer system 710 and data destination 715 can be a displaysystem. In this case, data source 705 provides pixel data according tohorizontal rows of pixels and data destination 715 receives pixel dataaccording to vertical columns of pixels, as described above.Checkerboard buffer system 710 provides the conversion.

Data source 705 can be implemented to provide pixel data according tovarious screen resolutions, such as a high definition (“HD”) resolutionof 1920×1080. While the discussion herein focuses on this HD resolution,alternative implementations can accommodate other resolutions. For an HDresolution signal, data source 705 provides pixel data for a progressivesignal (e.g., 1920×1080p). Data source 705 can be implemented to receivean interlaced signal (e.g., 1920×1080i) and provide a progressivesignal, such as by merging interlaced fields. In an alternativeimplementation, data source 705 provides an interlaced signal, providingpixel data for half the screen pixels (i.e., first field) and then pixeldata for the other half (i.e., second field). In another implementation,data source 705 provides pixel data using progressive segmented frames(“PSF,” by Sony Corporation of Japan, Inc.).

Each pixel has 32 bits of pixel data. In one implementation, 11 bits arefor red, 11 bits are for green, and 10 bits are for blue. Alternativeimplementations may have different allocations (e.g., 10 bits per color)or pixel depths (e.g., 8 or 24 bits per pixel). Where data source 705provides pixel data at 1920×1080p and 32 bits per pixel, the pixel rateis approximately 150 MP/S and the data rate from data source 705 isapproximately 600 MB/S. Accordingly, checkerboard buffer system 710stores pixel data from data source 705 at a data rate of approximately600 MB/S. To provide pixel data at a rate to support the sameresolution, 1920×1080p, checkerboard buffer system 710 outputs pixeldata to data destination 715 at a data rate of approximately 600 MB/S.

Data destination 715 can be a GLV system. A color GLV system includesthree GLV's: one for red, one for green, and one for blue. As describedabove, a GLV uses vertical columns of pixels to form an image(projecting one column at a time, typically left to right). In a colorGLV system, each GLV projects a column of pixels (e.g., 1088 pixels,though only 1080 may have corresponding pixel data from the video datasource) at a time. The three color columns are combined (such as usingmirrors and lenses) to form a single apparent column on the viewing area(not shown in FIG. 7). Accordingly, it is advantageous for the GLVsystem to receive pixel data according to vertical columns of pixels,rather than horizontal rows. Checkerboard buffer system 710 provides thepixel data to the GLV system corresponding to vertical columns ofpixels. In alternative implementations, data destination 715 can be someother video device that uses pixel data corresponding to verticalcolumns of pixels, such as a graphics card or a video image processor(e.g., for image transformations).

B. Illustrative Implementations of Checkerboard Buffers

This section describes several additional illustrative implementationsof checkerboard buffers. However, the described implementations areillustrative and those skilled in art will readily appreciate additionalimplementations are possible. The illustrative implementations aredescribed in separate numbered and labeled sections. However, compatibleaspects of the implementations can be combined in additionalimplementations.

1. Checkerboard Frame Buffer Using Two Memory Devices

FIG. 8 is a block diagram of a switching dual pixel frame bufferarchitecture 800 supporting the representations shown in FIGS. 6A, 6B,and 6C. Architecture 800 can implement checkerboard buffer system 710 inFIG. 7. A video source 805 provides pixel data to a first memory 810(e.g., first memory device 650 in FIG. 6B) and to a second memory 815(e.g., second memory device 675 in FIG. 6C) in parallel through a firstdata switch 820. A video destination 825 retrieves pixel data from firstmemory 810 and from second memory 815 in parallel through a second dataswitch 830.

First memory 810 and second memory 815 are separate memory devices suchas 32-bit wide 8 MB SDRAM's (e.g., 2M×32 SDRAM MT48LC2M32B2 by MicronTechnology, Inc.). The SDRAM is preferably fast enough to support thedata rate needed for the screen resolution, such as 125 MHZ or 150 MHZ.Other types of memory can also be used, such as DDR SDRAM (double datarate SDRAM) or SGRAM (synchronous graphics RAM). Memories 810 and 815each store half the pixel data of a particular frame, half for each rowof pixels and half for each column of pixels. In this implementation,pixel data for each pixel is stored in a separately addressable 32-bitmemory location, 32 bits per pixel. In alternative implementations,pixel data for each pixel could be split across memory locations orpixel data for multiple pixels could be stored in a single memorylocation.

Data switches 820 and 830 switch connections to alternate properlybetween memories 810 and 815, as described below. A first data bus 835is connected to first data switch 820, first memory 810, and second dataswitch 830. A second data bus 840 is connected to first data switch 820,second memory 815, and second data switch 830.

Video source 805 receives video data from another source (not shown),such as data source 705 in FIG. 7, a broadcast source, or a softwareapplication running on a computer system connected to video source 805.Video source 805 outputs pixel data for pixels two at a time, a firstpixel at a first source output 807 and a second pixel at a second sourceoutput 809. First data switch 820 has two states: providing the pixeldata at first source output 807 to first memory 810 and the pixel dataat second source output 809 to second memory 815; and providing thepixel data at first source output 807 to second memory 815 and the pixeldata at second source output 809 to first memory 810. Video source 805provides a control signal to first data switch 820 to control the stateof first data switch 820. This control signal can be based on theaddress provided by video source 805 (such as address bit A10 asdescribed below), or linked to the horizontal synchronization signal forthe frame received by video source 805. Video source 805 includes aflip-flop (not shown) to toggle the state of first data switch 820. Forexample, in one implementation, the horizontal synchronization signaltoggles the flip-flop, which in turn toggles the state of first dataswitch 820. In this way, the state of first data switch 820 changes witheach horizontal row of pixels. In another implementation, video source805 can provide all or part of the address to first data switch 820 forstate control.

Video destination 825 provides pixel data to a display system, such asdata destination 715 in FIG. 7 implemented as a GLV system. Videodestination 825 receives pixel data for pixels two at a time, a firstpixel at a first destination input 827 and a second pixel at a seconddestination input 829. Second data switch 830 has two states: providingthe pixel data from first memory 810 to first destination input 827 andthe pixel data from second memory 815 to second destination input 829;and providing the pixel data from second memory 815 to first destinationinput 827 and the pixel data from first memory 810 to second destinationinput 829. Video destination 825 provides a control signal to seconddata switch 830 to control the state of second data switch 830. Thiscontrol signal can be based on the address provided by video destination825 (such as bit C0 from a column counter, as described below). Videodestination 825 includes a flip-flop (not shown) to toggle the state ofsecond data switch 830. For example, in one implementation, a counter oran address bit toggles the flip-flop, which in turn toggles the state ofsecond data switch 830. In this way the state of second data switch 830changes with each vertical column of pixels. In another implementation,video destination 825 can provide all or part of the address to seconddata switch 830 for state control.

A source address bus 845 is connected to video source 805, a first input850 of a first address multiplexor 855, and a first input 860 of asecond address multiplexor 865. A first destination address bus 870 isconnected to video destination 825 and a second input 875 of firstaddress multiplexor 855. A second destination address bus 880 isconnected to video destination 825 and a second input 885 of secondaddress multiplexor 865. An output 890 of first address multiplexor 855is connected to first memory 810. An output 895 of second addressmultiplexor 865 is connected to second memory 815. Accordingly, the sameaddress is provided by video source 805 to both first memory 810 andsecond memory 815 to store pixel data while different addresses areprovided by video destination 825 to first memory 810 and second memory815 to retrieve data. Address multiplexors 855 and 865 receive controlsignals at control inputs (not shown) to control which input isconnected to the output. Memories 810 and 815 also receive controlsignals at control inputs (not shown) to control whether memories 810and 815 will read in data (write mode) or read out data (read mode). Inaddition, while clock lines are not shown in FIG. 8, architecture 800operates based on clock cycles so that pixel data can be processed fortwo pixels per clock cycle in support of the desired pixel rate. Inalternative implementations, as described below referring to FIGS. 18and 19, address generation and switching can be controlled by a memorycontroller.

Referring again to FIGS. 6A, 6B, and 6C, for frame 605, video source 805would supply pixel data for horizontal pixel pairs at source outputs 807and 809 in this sequence (first source output-second source output):0-1, 2-3, 4-5, 6-7, 8-9, 10-11, 12-13, 14-15, 16-17, 18-19, 20-21,22-23, 24-25, 26-27, 28-29, 30-31. Because of first data switch 820,first memory 810 would receive this sequence of pixel data: 0, 2, 4, 6,9, 11, 13, 15, 16, 18, 20, 22, 25, 27, 29, 31. Second memory 820 wouldreceive this sequence: 1, 3, 5, 7, 8, 10, 12, 14, 17, 19, 21, 23, 24,26, 28, 30. In contrast, for frame 605, first memory 810 would providepixel data for pixels in this sequence: 0, 16, 9, 25, 2, 18, 11, 27, 4,20, 13, 29, 6, 22, 15, 31. Second memory 815 would provide pixel datafor pixels in this sequence: 8, 24, 1, 17, 10, 26, 3, 19, 12, 28, 5, 21,14, 30, 7, 23. Because of second data switch 830, video destinationwould receive pixel data for vertical pixel pairs at destination inputs827 and 829 in this sequence (first destination input-second destinationinput): 0-8, 16-24, 1-9, 17-25, 2-10, 18-26, 3-11, 19-27, 4-12, 20-28,5-13, 21-29, 6-14, 22-30, 7-15, 23-31. Accordingly, pixel data for the32 pixels of frame 605 would be stored in 16 locations in two memories(810 and 815). The pixel data would be stored in 16 parallel operationsusing horizontal rows and retrieved in 16 parallel operations usingvertical columns.

In operation, memories 810 and 815 read in or store complementaryportions of a frame of pixels as pixel data from video source 805 andoutput the pixel data to video destination 825. Data switches 820 and830 ensure the proper alternation of connections to memories 810 and 815to provide the checkerboard pattern represented in FIG. 6A. As describedabove, pixel data for a frame of pixels from video source 805 is storedaccording to horizontal rows of pixels, and then the pixel data isretrieved according to vertical columns of pixels and provided to videodestination 825. After the pixel data for the entire frame has beenretrieved, pixel data for the next frame is stored, and so on. Somepixel data for the next frame may be buffered, such as in video source805, while pixel data for the previous frame is being retrieved. Asdescribed below, in alternative implementations, the storage andretrieval can be interleaved or occur in parallel.

FIG. 9 is a table 900 of addresses 905 and pixel numbers 910 for storinga 1920×1080 frame of pixel data. Pixel numbers 910 indicate for eachaddress 905 in two memories (e.g., memories 810 and 815 in FIG. 8) thepixel for which pixel data is stored at that address 905 in each memory.FIG. 9 shows only a small number of addresses for illustration. Ellipsesindicate intervening addresses or data. Some addresses are not used,indicated by “UNUSED.”

1024 memory locations 905 are allocated in each memory device to eachrow of 1920 pixels. For example, pixel data for pixel 0 is stored ataddress 0 in first memory 810 and pixel data for pixel 1 is stored ataddress 0 in second memory 815. Pixel data for horizontal pixel pair1918-1919 (i.e., the last two pixels of the first horizontal row) isstored at address 959 in first memory 810 and second memory 815,respectively. In the next horizontal row of pixels, pixel data forpixel-pair 1920-1921 is stored at address 1024 in second memory 815 andfirst memory 810, respectively. Addresses 960 to 1023 are not used forstoring pixel data in this implementation. A similar pattern is followedfor each horizontal row, so that the address for the first pixel pair ofeach horizontal row is a multiple of 1024 (i.e., 0, 1024, 2048, 3072, .. . , 1104896).

As described below, it is convenient for the address of the memorylocation for the first pixel pair of each horizontal row to be a powerof 2 so that addresses can be generated by merging counters. In HDresolution, each horizontal row has 1920 pixels. Each memory storespixel data for half of the pixels in a horizontal row and one-half of arow is 960 pixels. The next largest power of 2 over 960 is 1024, sopixel data for each horizontal row of 1920 pixels is allocated 1024memory locations.

Before describing the overall operation of storing pixel data tomemories 810 and 815, it will be useful to describe examples ofimplementations of how addresses are calculated for storing pixel data.Video source 805 generates addresses to store pixel data for horizontalpixel pairs according to horizontal rows of pixels. In an HD resolutionimplementation, video source 805 stores pixel data for pixel pairs inthis sequence: 0-1, 2-3, 4-5, and so on. Referring to FIG. 9, videosource 805 generates addresses in the following sequence (one addressfor each pixel pair): 0, 1, 2, . . . , 959, 1024, 1025, . . . , 1983,2048, 2049, and so on. As described above, pixel data for pixels of ahorizontal pixel pair are stored at the same address in respectivememory devices, switching memory devices with each row.

In one implementation, video source 805 includes an address counter, andincrements the counter by 1 for pixel data for each pixel pair output tosource outputs 807 and 809. For example, for pixels 0 and 1, the counteris 0. For pixels 2 and 3, the counter is 1. In an alternativeimplementation, the counter can be incremented by 1 for pixel data foreach pixel, and the lowest order bit of the counter is dropped beforethe counter value is used as an address. The value of the counter isoutput to source address bus 845.

FIG. 10 is a representation of an address counter 1005 for video source805. Counter 1005 has 21 bits labeled A0 to A20, enough bits to addressevery location in memories 810 and 815. As described above, memories 810and 815 can each be implemented as 32-bit wide 8 MB SDRAM's and so eachcan have 2²¹ (2,097,152) four-byte locations (to accommodate 32 bits perpixel). In HD resolution, one frame has 1080 horizontal rows, so thereare 1,105,856 locations to address (1024×1079+960=1105856). Accordingly,counter 1005 has 21 bits (20 bits would range from 0 to 1,048,575). Asdescribed above, a GLV typically has 1088 pixels, creating an extraeight rows of pixels, so memories 810 and 815 may store constant data(such as black) for these extra 8 rows of pixels when supplying pixeldata to a GLV.

Because the first pixel pair of each horizontal row has an address thatis a multiple of 1024, the first ten bits of counter 1005 (starting fromthe lowest order bit, A0 . . . A9; ten bits can express 0 to 1023) canbe viewed as a column counter indicating a pixel pair in a horizontalrow and the upper eleven bits (A10 . . . A20) can be viewed as a rowcounter indicating a horizontal row. In this view, combining the twocounters produces an address. Furthermore, as video source 805increments the counter, the eleventh bit (A10) of the address, which canbe viewed as the lowest order bit of the row counter, changes at thebeginning of each horizontal row. Accordingly, video source 805 can usethis bit to toggle a flip-flop controlling the state of first dataswitch 820, causing the alternation between memories 810 and 815 instoring pixels.

FIG. 11 is a flowchart of generating addresses for storing pixel datafor a frame of pixels in an HD resolution implementation using 1024locations in each memory per row of pixels. At the beginning of a frame,video source 805 resets counter 1005 to 0, block 1105. Video source 805provides the value of counter 1005 to source address bus 845, block1110. Video source 805 increments counter 1005 by 1, block 1115. Videosource 805 compares the value of counter 1005 to a maximum frame valueto check if the last pixel pair in the frame has been processed, block1120. The maximum frame value depends on the implementation. If themaximum frame value has been reached, address generation for the currentframe is complete, block 1125. If the maximum frame value has not beenreached, video source 805 compares the value of the low order 10 bits ofcounter 1005 to a maximum row value (e.g., 960) to check if the lastpixel in a horizontal row has been processed, block 1130. If the maximumrow value has been reached, video source 805 increments counter 1005 by64 (e.g., from 960 to 1024, or from 1984 to 2048), block 1135, andreturns to block 1110. In an alternative implementation, video source805 increments the counter by 64 based on receiving the horizontalsynchronization signal. If the maximum row value has not been reached,video source 805 proceeds with block 1110. When storing pixel data for anew frame, video source 805 starts generating addresses again beginningwith block 1105.

FIG. 12 is a flowchart of storing pixel data. To store pixel data,memories 810 and 815 are put in write mode and address multiplexors 855and 865 are set to connect first inputs 850 and 860 to outputs 890 and895, respectively, block 1205. Video source 805 provides pixel data fora first pixel to first source output 807, such as pixel 0 in FIG. 6A,and pixel data for a second pixel to second source output 809, such aspixel 1 in FIG. 6A, block 1210. Video source 805 also provides anaddress to source address bus 845, which in turn provides the address tofirst input 850 of first address multiplexor 855, and first input 860 ofsecond address multiplexor 865, block 1215. As described above, videosource 805 uses a counter to calculate the address, and increments thecounter by 1 for each pixel pair. At the beginning of each frame, videosource 805 resets this counter.

Video source 805 provides a control signal to first data switch 820 tocontrol which pixel data to send to which memory, block 1220.Alternatively, video source 805 provides a control signal to first dataswitch 820 when the state of first data switch 820 is to change. Videosource 805 causes first data switch 820 to change states when pixel datafor a complete row of pixels has been stored. As described above, videosource 805 toggles a flip-flop connected to first data switch 820, suchas by using one of the address bits (e.g., bit A10). In one state, firstdata switch 820 provides pixel data from first source output 807 tofirst data bus 835 and pixel data from second source output 809 tosecond data bus 840. In the other state, first data switch 820 providespixel data from first source output 807 to second data bus 840 and pixeldata from second source output 809 to first data bus 835. In anotherimplementation, video source 805 toggles a flip-flop connected to firstdata switch 820 based on the horizontal synchronization signal or thecounter value (e.g., when the counter equals a multiple of 960) tochange states.

First data bus 835 provides its pixel data to first memory 810 andsecond data bus 840 provides its pixel data to second memory 815, block1225. Address multiplexors 855 and 865 provide the address from sourceaddress bus 845 to first memory 810 and second memory 815, block 1230.First memory 810 stores the pixel data on first data bus 835 at theaddress supplied by address multiplexor 855 from video source 805 andsecond memory 815 stores the pixel data on second data bus 840 at thesame address, block 1235. Two pixels have been stored in parallel in tworespective memories using the same address. Referring to FIGS. 6A, 6B,and 6C, pixel 0 and pixel 1 are stored at the same time at the sameaddress in first memory device 650 and second memory device 675,respectively. To store pixel data for the next two pixels, video source805 returns to block 1210, or to block 1205 to restore the state ofarchitecture 800 for storage.

Before describing the overall operation of retrieving pixel data frommemories 810 and 815, it will be useful to describe examples ofimplementations of how addresses are calculated for retrieving pixeldata. Video destination 825 retrieves pixel data corresponding tovertical columns of pixels, but video source 805 has stored pixel datain memories 810 and 815 using horizontal rows of pixels. Accordingly,pixel data for vertically adjacent pixels do not have adjacent memoryaddresses. For example, referring to FIGS. 6A, 6B, and 6C, pixels 0, 8,16, and 24 are a series of vertically adjacent pixels, forming avertical column. However, pixel data for pixels 0 and 16 are not atneighboring addresses in first memory device 650 (pixel data for pixels15 and 18 are at neighboring addresses to pixel data for pixel 16).Furthermore, pixel data for the vertical pixel pairs retrieved by videodestination 825 do not have the same address, in contrast with thehorizontal pixel pairs in storing pixels. For example, video destination825 would retrieve pixels 0 and 8 in parallel from memory devices 650and 675, respectively, but pixel 0 is at address 0 in first memorydevice 650 and pixel 8 is at address 4 in second memory device 675.

In an HD resolution implementation, video destination 825 retrievespixel data for vertical pixel pairs in this sequence: 0-1920, 3840-5760,. . . , 1-1921, 3841-5761, and so on. Video destination 825 generates apair of addresses for each vertical pixel pair. One address is suppliedto first memory 810 and one address is supplied to second memory 815.Referring to FIG. 9, video destination 825 generates addresses in thefollowing sequence: 0-1024, 2048-3072, . . . , 0-1024, 2048-3072, . . ., 1-1025, 2049-3073, and so on. The same sequence of addresses can beused for two columns of pixels, however, which memory receives whichaddress changes with each column. In the first column, first memory 810receives the first address in the pair of addresses, and in the secondcolumn, first memory 810 receives the second address. For example, forthe first vertical pixel pair in the first column, first memory 810receives address 0 (pixel 0) and second memory 815 receives address 1024(pixel 1920). For the first vertical pixel pair in the second column,first memory 810 receives address 1024 (pixel 1921) and second memory815 receives address 0 (pixel 1).

FIG. 13 is a representation of generating destination addresses. Videodestination 825 includes two address counters: a row counter 1305, and acolumn counter 1310. Row counter 1305 indicates horizontal rows andcolumn counter 1310 indicates vertical columns. Row counter 1305 has 11bits, ranging from 0 to 2047, to accommodate all 1080 horizontal rows inthe frame. Column counter 1310 has 11 bits, ranging from 0 to 2047, toaccommodate all 1920 vertical columns in the frame. In combination, thecounters can indicate a pixel in the frame. Video destination 825combines the values of row counter 1305 and column counter 1310 toproduce a first destination address 1315. The upper 10 bits of columncounter 1310 form the low order bits of first destination address 1315and row counter 1305 forms the high order bits. As described below, bitC0 is not used in the destination addresses. Video destination 825 alsocombines the values of row counter 1305 and column counter 1310 toproduce a second destination address 1320. The upper 10 bits of columncounter 1310 form the low order bits of second destination address 1320.The eleventh bit (A10) of second destination address 1320 is thecomplement of the low order bit (R0) of row counter 1305 (i.e., if R0equals 0, A10 equals 1, and if R0 equals 1, A10 equals 0). Thiscomplement causes the second destination address 1320 to be 1024 greaterthan (i.e., one row ahead) or 1024 less than (i.e., one row behind) thefirst destination address 1315. The remaining bits of row counter 1305(R1 to R10) form the remaining high order bits of second destinationaddress 1320 (A11 to A20). In another implementation, video destination825 uses a pair of counters, offset by the width of the frame, togenerate first and second destination addresses. As described above,memories 810 and 815 can be implemented each as 8 MB SDRAM's, having2,097,152 four-byte locations. In addition, pixel data is stored inblocks of 960 sequential four-byte locations, representing halves ofhorizontal rows. Accordingly, destination addresses 1315 and 1320 eachhave 21 bits, ranging from 0 to 2,097,151.

The low order bit of column counter 1310 (bit C0) is not used indestination addresses 1315 and 1320. As described above, pixel data foreach of the pixels in a horizontal pixel pair is stored in a respectivememory device at the same address and so the same address can be used toretrieve pixel data for either pixel. Referring to table 900 in FIG. 9,address 0 can be used to access pixel data for pixel 0 or for pixel 1.While column counter 1310 differentiates between pixels 0 and 1,destination addresses 1315 and 1320 do not. To access pixel data forpixel 0 or pixel 1, address 0 is supplied to first memory 810 or secondmemory 815, respectively. Accordingly, bit C0, the lowest order bit ofcolumn counter 1310, is not used in destination addresses 1315 and 1320.In an alternative implementation, destination addresses 1315 and 1320include bit C0 of column counter 1310 (and so destination addresses 1315and 1320 have 22 bits), but memories 810 and 815 ignore this bit andtreat the upper 21 bits as the full address.

However, bit C0 can be used to indicate which column of pixels is beingprocessed by video destination 825. For example, C0 is 0 foreven-numbered columns (e.g., columns 0, 2, 4, etc.) and C0 is 1 forodd-numbered columns (e.g., columns 1, 3, 5, etc.). Accordingly, videodestination 825 can use bit C0 to control second data switch 830.Because bit C0 changes with each new column, video destination 825 canuse bit C0 to toggle a flip-flop to toggle the state of second dataswitch 830. For example, for the first column of pixels (column 0), C0is 0 and so pixel data from first memory 810 is supplied to firstdestination input 827 and pixel data from second memory 815 is suppliedto second destination input 829. Referring to table 900 in FIG. 9, videodestination 825 would receive pixel data for vertical pixel pair 0-1920from first and second memories 810 and 815, respectively. For the secondcolumn of pixels (column 1), C0 is 1 and the state of second data switch830 changes. Pixel data from first memory 810 is supplied to seconddestination input 829 and pixel data from second memory 815 is suppliedto first destination input 827. Referring to table 900 in FIG. 9, videodestination 825 would receive pixel data for vertical pixel pair 1-1921from second and first memories 815 and 810, respectively.

FIG. 14 is a flowchart of generating addresses for retrieving pixel datafrom a first memory for a frame of pixels in an HD resolutionimplementation using 1024 locations in each memory per row of pixels. Atthe beginning of a frame, video destination 825 resets row counter 1305to 0 and column counter 1310 to 0, block 1405. Video destination 825generates first destination address 1315 and second destination address1320 as described above. Video destination 825 provides firstdestination address 1315 to first destination address bus 870 and seconddestination address 1320 to second destination address bus 880, block1410. Video destination 825 increments row counter 1305 by 2, block1415. Video destination 825 compares the value of row counter 1305 to amaximum row value (e.g., 1080) to check if the end of the verticalcolumn has been reached, block 1420. If row counter 1305 is less thanthe maximum row value, video destination 825 proceeds to block 1410. Ifrow counter 1305 is greater than or equal to the maximum row value,video destination 825 increments column counter 1310 by 1, block 1425.Video destination 825 compares the value of column counter 1310 to amaximum column value (e.g., 1920) to check if the end of the frame hasbeen reached, block 1430. If the maximum column value has been reached,address generation for the current frame is complete, block 1435. If themaximum column value has not been reached, video destination 825 resetsrow counter 1305, block 1440, and proceeds to block 1410. At thebeginning of each column, the first destination address is set tocorrespond to the pixel in alternately the first or second horizontalrow, such as by setting the row counter to the value of bit C0 of columncounter 1310. When retrieving pixel data for a new frame, videodestination 825 starts generating addresses again beginning with block1405.

In an alternative implementation, video destination 825 provides firstdestination address 1315 and second destination address 1320 to memories810 and 815 in alternation with each column of pixels. At the beginningof each column, the row counter is reset to 0. Bit C0 can be used tocontrol which destination address is sent to which destination addressbus and so to which memory. For example, for pixels in the first column(and other even-numbered columns, where the first column is consideredcolumn 0), where C0 is 0, first memory 810 receives first destinationaddress 1315 and retrieves pixel data for pixels in even-numbered rows.Second memory 815 receives second destination address 1320 and retrievespixel data for pixels in odd-numbered rows. For pixels in the secondcolumn (and other odd-numbered columns), where C0 is 1, first memory 810receives second destination address 1320 and retrieves pixel data forpixels in odd-numbered rows. Second memory 815 receives firstdestination address 1315 and retrieves pixel data for pixels ineven-numbered rows. The alternation of destination addressesaccommodates this retrieval pattern.

FIG. 15 is a flowchart of retrieving pixel data. To retrieve pixel data,memories 810 and 815 are put in read mode and address multiplexors 855and 865 are set to connect second inputs 875 and 885 to outputs 890 and895, respectively, block 1505. Video destination 825 generates firstdestination address 1315 and second destination address 1320, asdescribed above, block 1510. Video destination 825 provides first andsecond destination addresses to first and second destination addressbuses 870 and 880, as described above, which in turn provide thedestination addresses to address multiplexors 855 and 865, block 1515.Video destination 825 provides a control signal, as described above, tosecond data switch 830 for state control, block 1520. Alternatively,video destination 825 provides a control signal to second data switch830 when the state of second data switch 830 is to change. First addressmultiplexor 855 provides the address from first destination address bus870 to first memory 810 through output 890 and second addressmultiplexor 865 provides the address from second destination address bus880 to second memory 815 through output 895, block 1525. First memory810 provides pixel data stored at the received address to first data bus835 and second memory 815 provides pixel data stored at the receivedaddress to second data bus 840, and data buses 835 and 840 provide thepixel data to second data switch 830, block 1530.

Second data switch 830 uses the control signal received from videodestination 825 to control which pixel data to send to which destinationinput of video destination 825, block 1535. As described above, in oneimplementation, video destination 825 uses one of the counter bits forcontrolling second data switch 830, such as bit C0 of column counter1310 in FIG. 13. When C0 is 0, indicating an even-numbered verticalcolumn, second data switch 830 provides pixel data from first data bus835 to first destination input 827 and pixel data from second data bus840 to second destination input 829. When C0 is 1, indicating anodd-numbered vertical column, second data switch 830 provides pixel datafrom second data bus 840 to first destination input 827 and pixel datafrom first data bus 835 to second destination input 829. Two pixels havebeen retrieved in parallel from two memories using different addresses.Referring to FIGS. 6A, 6B, and 6C, pixel 0 and pixel 8 would beretrieved from first memory device 650 and second memory device 675,respectively, at the same time from addresses 0 and 4, respectively. Toretrieve pixel data for the next two pixels, video destination 825returns to block 1510, or to block 1505 to restore the state ofarchitecture 800 for retrieval.

2. Checkerboard Frame Buffer Using Two Memory Devices, 960 MemoryLocations Per Row of 1920 Pixels

In another HD resolution implementation, rather than allocating 1024memory locations in each memory device to each row of 1920 pixels (960horizontal pixel pairs), the checkerboard frame buffer allocates 960memory locations in each memory device to each row of 960 horizontalpixel pairs. This allocation creates fewer gaps in memory and so usesless memory for the same amount of pixel data. The structure andoperation of this implementation is similar to architecture 800 in FIG.8, as described above, however, address generation is different, asdescribed below. In implementations for different screen resolutions,the checkerboard buffer can allocate in each memory device a number ofmemory locations for each row of pixels equal to half the number ofpixels in a row.

FIG. 16 is a table 1600 of addresses 1605 and pixel numbers 1610 forstoring a 1920×1080 frame of pixel data. Similar to table 900 in FIG. 9,pixel numbers 1610 indicate for each address 1605 in two memories (e.g.,memories 810 and 815 in FIG. 8) the pixel for which pixel data is storedat that address 1605 in each memory. FIG. 16 shows only a small numberof addresses for illustration. Ellipses indicate intervening addressesor data.

960 memory locations are allocated in each memory device to each row of1920 pixels. For example, pixel data for pixel 0 is stored at address 0in first memory 810 and pixel data for pixel 1 is stored at address 0 insecond memory 815. Pixel data for horizontal pixel pair 1918-1919 (i.e.,the last two pixels of the first horizontal row) is stored at address959 in first memory 810 and second memory 815, respectively. In the nexthorizontal row of pixels, pixel data for pixel-pair 1920-1921 is storedat address 960 in second memory 815 and first memory 810, respectively.In contrast with table 900, in table 1600, there are no unused addressesbetween the address storing pixel data for the pixel at the end of ahorizontal row and the address storing pixel data for the pixel at thebeginning of the next row in a frame.

As described above, video source 805 generates addresses to store pixeldata for horizontal pixel pairs according to horizontal rows of pixels,however, in this implementation, the sequence of addresses is differentfrom the sequence described above. Video source 805 stores pixel datafor pixel pairs in this sequence: 0-1, 2-3, 4-5, and so on. Referring toFIG. 16, video source 805 generates addresses in the following sequence(one address for each pixel pair): 0, 1, 2, . . . , 959, 960, 961, andso on.

Video source 805 uses a counter to generate source addresses. Thecounter ranges from 0 to one less than one-half of the numbers of pixelsin one frame (recalling that each memory stores pixel data for half thepixels in one frame; (1920*1080/2)−1=1,036,799). Video source 805generates addresses following a similar process as shown in FIG. 11,however, video source 805 does not cause the counter to increment by 64at the end of each row, and instead proceeds with the next sequentialaddress (e.g., from 959 to 960, rather than from 959 to 1024).

As described above, video source 805 also sends a control signal tofirst data switch 820 for state control. Video source 805 causes thestate to change at the end of each horizontal row, such as by toggling aflip-flop based on the horizontal synchronization signal or when thecounter reaches a multiple of 960.

Similar to the destination address generation described above, in thisimplementation, video destination 825 generates addresses to retrievepixel data for vertical pixel pairs according to vertical columns ofpixels, however, the sequence of addresses is different from thesequence described above. Video destination 825 retrieves pixel data forvertical pixel pairs in this sequence: 0-1920, 3840-5760, . . . ,1-1921, 3841-5761, and so on. Referring to FIG. 16, video destination825 generates addresses in the following sequence: 0-960, 1920-2880, . .. , 0-960, 1920-2880, . . . , 1-961, 1921-2881, and so on. As describedabove, the same sequence of addresses can be used for two columns ofpixels, however, which memory receives which address changes with eachcolumn. In the first column, first memory 810 receives the first addressin the pair of addresses, and in the second column, first memory 810receives the second address. For example, for the first vertical pixelpair in the first column, first memory 810 receives address 0 (pixel 0)and second memory 815 receives address 960 (pixel 1920). For the firstvertical pixel pair in the second column, first memory 810 receivesaddress 960 (pixel 1921) and second memory 815 receives address 0 (pixel1).

Various implementations can be used to generate the destinationaddresses. In one implementation, video destination 825 also uses acounter ranging from 0 to one less than one-half of the numbers ofpixels in one frame to generate destination addresses. The counterincrements by the number of pixels in a horizontal row (i.e., thewidth), such as 1920 in a HD resolution implementation. The firstdestination address would be the value of the address counter. Thesecond destination address would be equal to the first destinationaddress plus 960 for even-numbered columns and equal to the firstdestination address minus 960 for odd-numbered columns. In thisimplementation, first memory 810 always receives the first destinationaddress and second memory 815 always receives the second destinationaddress. The counter is incremented after each vertical pixel pair(e.g., referring to FIG. 6B, to access pixel data for pixel pair 0 and8, and then for pixel pair 16 and 24, both in the first column). At thebeginning of each new column of pixels, the counter is reset to 0 (foreven columns) or 960 (for odd columns) plus a value equal to half of thenumber of columns of pixels completed. For example, using a separatecolumn counter to count columns, the address counter can be reset to avalue derived by dividing the number of columns completed by 2 andadding the quotient to the remainder times 960. This address counterwould be reset in this sequence: 0, 960, 1, 961, and so on. The lastpixel pair of a column is indicated by the counter meeting or exceedinga threshold, such as the address of the first pixel pair in the next tolast horizontal row (e.g., 1078*960=1,034,880). In addition, at thebeginning of each column, video destination 825 toggles the state ofsecond data switch 830.

In another implementation, one memory device receives the value of thecounter as an address, and one memory device receives the value of thecounter plus half the width (e.g., 960). Which memory device receivesthe value of the counter and which receives the value of the counterplus half the width alternates with each column of pixels. For example,referring to FIGS. 6A, 6B, and 6C, for the first pixel pair, firstmemory device 650 would receive address 0 (the value of the counter;pixel 0) and second memory device 675 would receive address 4 (the valueof the counter plus 4; pixel 8). The counter would be incremented by thewidth to 8. For the next pixel pair, first memory device 650 wouldreceive address 8 (pixel 16) and second memory device 675 would receiveaddress 12 (pixel 24). For the next column, the counter would be resetto 0. Second memory device 675 would receive address 0 (the value of thecounter; pixel 1) and first memory device 650 would receive address 4(the value of the counter plus 4; pixel 9). The counter would beincremented to 8. For the next pixel pair, second memory device 675would receive address 8 (pixel 17) and first memory device 650 wouldreceive address 12 (pixel 25). For the third column, the counter wouldbe reset to 1. First memory device 650 would receive addresses 1 and 9(pixels 2 and 18) and second memory device 675 would receive addresses 5and 13 (pixels 10 and 26). This pattern continues throughout theremainder of the frame.

In another implementation, destination addresses are mathematicallyderived from a row counter and a column counter, such as by multiplyingthe row counter value by half of the width of a frame and adding thecolumn counter value. In yet another implementation, a row counter and acolumn counter can be used as indices into a look-up table ofdestination addresses.

3. Checkerboard Frame Buffer Using Two Memory Devices and MemorySections

In another implementation, the memory address space is divided into twosections. This division applies to both memory devices. As describedabove referring to double-buffering, one section of each memory is usedfor storing pixel data and the other section for retrieving pixel data.The sections switch roles with each frame. The operation of architecture800 of FIG. 8 modified to use memory sections is described below.

Memories 810 and 815 each store pixel data for complementary halves oftwo frames at a time. Memories 810 and 815 are divided in half. Forexample, where memories 810 and 815 are 32-bit wide 8 MB SDRAM's, afirst section of addresses (0 through 1,048,575) is for one frame and asecond section of addresses (1,048,576 through 2,097,151) is for anotherframe. As described above, in HD resolution, half of one frame has1,036,800 pixels and so a 32-bit wide 8 MB SDRAM is sufficiently largefor half of each of two frames. However, where 1024 32-bit locations areused for pixel data for each row of pixels, half of each of two framesdoes not fit into a 32-bit 8 MB SDRAM, and so either 960 32-bitlocations for each row would be used or a larger memory (e.g., 16 MB)would be required. While one frame is being stored in one section,another frame is being retrieved from the other section, such as inalternating series of read and write operations. After processing theseframes has completed, pixel data for a new frame is read into thesection storing the frame just read out, and pixel data for the framejust stored is read out. In this way, the sections alternate betweenreading and writing. To generate addresses for storing pixels, videosource 805 alternates between initializing the counter to 0 and to themiddle of the available address space (e.g., 1,048,576) with each frameto alternate between the two sections of memory. Similarly, videodestination 825 alternates between resetting its counter to 0 and themiddle of the available address space with each frame to be retrieved.

In addition, pixel data can be stored and retrieved in alternation forblocks of pixels smaller than an entire frame. For example, in oneimplementation, video source 805 and video destination 825 each includea FIFO buffer. As video source 805 receives pixel data, video source 805fills its FIFO buffer. At regular intervals, such as when the FIFObuffer is full or after pixel data for a number of pixels has beenplaced in the FIFO buffer, video source 805 causes pixel data for ablock of pixels from its FIFO buffer, such as the first 32 pixels in theFIFO buffer, to be stored and generates the appropriate addresses for aseries of write operations. After this block has been stored videosource 805 passes control to video destination 825. Video destination825 generates addresses, retrieves pixel data for a block of pixels,such as 32 pixels, in a series of read operations from memories 810 and815, and stores the pixel data in its own FIFO buffer. Video destination825 then passes control back to video source 805, and so on. Videosource 805 and video destination 825 preserve the counter values betweenblocks to accommodate this block-based processing.

FIG. 17 is a flowchart of reading and writing blocks of pixels usingmemory sections. When video source 805 has received pixel data for ablock of pixels from a first frame, such as 32 pixels, video source 805stores the pixel data in the first sections (e.g., starting from address0) of memories 810 and 815 in a series of write operations, block 1705.Video destination 825 takes control (or video source 805 passes controlto video destination 825) and retrieves pixel data for a block of pixelsfrom a previous frame, such as 32 pixels, from the second sections(e.g., starting from the middle of the memory address space, such as1,048,576) of memories 810 and 815, block 1710. Initially, while thevery first frame is being stored to the first sections, the secondsections will have undefined data and so pixel data retrieved from thesecond sections during this first iteration will most likely not producea valid image, but this situation will only last while the first frameis being stored. Video source 805 takes control (or video destination825 passes control to video source 805) and checks whether the end ofthe frame being stored has been reached, block 1715. If the end of theframe has not been reached, video source 805 returns to block 1705 andstores pixel data for the next block of pixels in the first sections ofmemories 810 and 815. If the end of the frame has been reached, videosource 805 stores pixel data for the next block of pixels from the nextframe in the second sections of memories 810 and 815, block 1720. Videodestination 825 takes control and retrieves pixel data for a block ofpixels from the first sections of memories 810 and 815, block 1725.Video source 905 takes control and checks whether the end of the framebeing stored has been reached, block 1730. If the end of the frame hasnot been reached, video source 805 returns to block 1720 and storespixel data for the next block of pixels in the second sections ofmemories 810 and 815. If the end of the frame has been reached, videosource 805 returns to block 1705 and stores pixel data for the firstblock of pixels from the next frame in the first sections of memories810 and 815. This alternation continues until video source 805 does notreceive pixel data.

4. Checkerboard Frame Buffers Using Two Memory Devices and a MemoryController

As described above, architecture 800 controls addressing and data flowusing video source 805, video destination 825, first and second dataswitches 820 and 830, and address multiplexors 855 and 865. A memorycontroller can be used to control addressing and data flow to and fromthe memory devices of a checkerboard buffer.

FIG. 18 is a block diagram of another implementation of a switching dualpixel frame buffer architecture 1800. Architecture 1800 is similar toarchitecture 800 of FIG. 8, but a memory controller 1855 provides dataand addresses to memories 1810 and 1815. Memory controller 1855 receivespixel data from video source 1805 to store in memories 1810 and 1815.Memory controller 1855 retrieves pixel data from memories 1810 and 1815and provides the pixel data to video destination 1825. Memory controller1855 replaces address multiplexors 855 and 865 in FIG. 8. Memorycontroller 1855 receives signals from video source 1805 and videodestination 1825 through control lines 1845 and 1870, respectively,indicating whether pixel data is to be stored to or retrieved frommemories 1810 and 1815. Memory controller 1855 generates addresses andsupplies these addresses along with control signals to memories 1810 and1815. Accordingly, memory controller 1855 controls address generationrather than video source 1805 and video destination 1825, as comparedwith architecture 800 of FIG. 8. In addition, as noted above withrespect to FIG. 8, architecture 1800 operates based on clock cycles sothat pixel data can be processed for two pixels per clock cycle insupport of the desired pixel rate. In an alternative implementation,memory controller 1855 also controls the states of data switches 1820and 1830, rather than video source 1805 and video destination 1825 as inFIG. 8.

FIG. 19 is a block diagram of another implementation of a switching dualpixel frame buffer architecture 1900. Architecture 1900 is similar toarchitecture 1800 of FIG. 18, but a memory controller 1955 includes dataswitch functionality and so replaces data switches 1820 and 1830 in FIG.18. Memory controller 1955 receives pixel data from video source 1905through data buses 1907 and 1909 to store in memories 1910 and 1915.Memory controller provides pixel data to video destination 1925 throughdata buses 1927 and 1929 retrieved from memories 1910 and 1915. Eachdata bus provides pixel data for one pixel at a time, as in architecture800 of FIG. 8 or architecture 1800 of FIG. 18. Memory controller 1955receives signals from video source 1905 and video destination 1925through control lines 1930 and 1935, respectively, indicating whetherpixel data is to be stored to or retrieved from memories 1910 and 1915.Memory controller 1955 generates addresses and supplies these addressesalong with control signals to memories 1910 and 1915 through addressbuses 1960 and 1965, respectively. When storing pixel data, memorycontroller 1955 provides pixel data to memories 1910 and 1915 throughdata buses 1970 and 1975, respectively. When retrieving pixel data,memory controller 1955 receives pixel data from memories 1910 and 1915through data buses 1970 and 1975, respectively. Accordingly, memorycontroller 1955 controls address generation and where pixel data foreach pixel is sent (similar to data switches 820 and 830 of FIG. 8). Inaddition, as noted above with respect to FIG. 8, architecture 1900operates based on clock cycles so that pixel data can be processed fortwo pixels per clock cycle in support of the desired pixel rate.

5. Checkerboard Frame Buffer Using Four Memory Devices

Increasing from one memory device to two memory devices in a framebuffer can provide an improvement in memory bandwidth. Similarly,increasing from the two memory devices of architecture 800 in FIG. 8 tofour memory devices can provide a further increase in bandwidth.

FIG. 20 is a block diagram of a switching dual pixel frame bufferarchitecture 2000 having four memory devices: first memory 2010, secondmemory 2015, third memory 2017, and fourth memory 2019. The memorydevices are used in two alternating banks for storing and retrievingpixel data a frame at a time. For example, a first frame of pixel datais stored, two pixels at a time, in first memory 2010 and second memory2015, such as described in FIG. 12. A second frame of pixel data is thenstored in third memory 2017 and fourth memory 2019. While the secondframe is being stored, the first frame of pixel data is retrieved fromfirst memory 2010 and second memory 2015, two pixels at a time, such asdescribed in FIG. 15. Accordingly, pixel data for the first frame isretrieved at the same time pixel data for the second frame is stored(i.e., during the same clock cycle). During every clock cycle, pixeldata for one frame is stored and pixel data previously stored isretrieved. For the next frames, the memory banks are switched. The thirdframe of pixel data is stored in first memory 2010 and second memory2015, while the second frame pixel data is retrieved from third memory2017 and fourth memory 2019. This alternation between memory bankscontinues as long as frames are supplied to video source 2005. Becauseof the increased memory size and simultaneous storage and retrieval, anHD resolution implementation of architecture 2000 using four 32-bit wide8 MB SDRAM's can be implemented allocating 1024 locations in each memoryto each row of pixels and without internally dividing each of the memorydevices into sections.

Architecture 2000 is similar to architecture 800 in FIG. 8, except thatarchitecture 2000 has additional hardware to support switching betweenthe two banks of memory devices: a 4×4 data switch 2032, and twoadditional address multiplexors 2067 and 2069. 4×4 switch 2032 isconnected to memories 2010, 2015, 2017, and 2019 by memory buses 2096,2097, 2098, and 2099, respectively. 4×4 data switch 2032 has two states:(A) connecting data buses 2035 and 2040 to memories 2010 and 2015,respectively, and data buses 2042 and 2044 to memories 2017 and 2019,respectively; and (B) connecting data buses 2035 and 2040 to memories2017 and 2019, respectively, and data buses 2042 and 2044 to memories2010 and 2015, respectively. Accordingly, in state A while memory buses2096 and 2097 are providing pixel data to be stored to first memory 2010and second memory 2015, respectively, memory buses 2098 and 2099 areproviding pixel data retrieved from third memory 2017 and fourth memory2019, respectively. Conversely, in state B while memory buses 2096 and2097 are providing pixel data retrieved from first memory 2010 andsecond memory 2015, respectively, memory buses 2098 and 2099 areproviding pixel data to be stored to third memory 2017 and fourth memory2019, respectively. 4×4 switch 2032 receives a control signal (notshown) to switch between states, such as from video source 2005. Videosource 2005 toggles the control signal after completing storing pixeldata for a frame. In one implementation, 4×4 switch 2032 is connected toa flip-flop that is triggered by a vertical synchronization signalsupplied by video source 2005. Third address multiplexor 2067 and fourthaddress multiplexor 2069 are used in the same manner as first addressmultiplexor 2055 and second address multiplexor 2065, as described abovereferring to address multiplexors 855 and 865 in FIGS. 8, 12, and 15. Inaddition, while clock lines are not shown in FIG. 20, architecture 2000operates based on clock cycles so that pixel data can be processed forfour pixels per clock cycle in support of the desired pixel rate.

FIG. 21 is a flowchart of storing and retrieving pixel data in parallelin architecture 2000 of FIG. 20. When a first frame of pixel databecomes available to video source 2005, video source 2005 sets 4×4switch 2032 to state A (pixel data to be stored to first memory 2010 andsecond memory 2015, pixel data to be retrieved from third memory 2017and fourth memory 2019), block 2105. Video source 2005 stores the firstframe of pixel data, two pixels at a time, in first memory 2010 andsecond memory 2015, as described above referring to FIGS. 10, 11, and12, and video destination 2025 retrieves pixel data from third memory2017 and fourth memory 2019, as described above referring to FIGS. 13,14, and 15, block 2110. Initially, valid pixel data has not been storedin memories 2017 and 2019, and so pixel data retrieved during the firstloop will not produce a valid image. After a frame of pixel data hasbeen stored, video source 2005 sets 4×4 switch 2032 to state B (pixeldata to be retrieved from first memory 2010 and second memory 2015,pixel data to be stored to third memory 2017 and fourth memory 2019),block 2115. A frame of pixel data is stored by video source 2005 andanother frame is retrieved by video destination 2025 according to thestate of 4×4 switch 2032, as described above, block 2120. After a frameof pixel data has been stored, video source 2005 returns to block 2105and sets 4×4 switch 2032 to state A. When a new frame is not availableto video source 2005, storing and retrieving pixels from architecture2000 is complete. When a new frame later becomes available, video source2005 begins at block 2105 again.

6. Checkerboard Frame Buffers Using Four Memory Devices and a MemoryController

Similar to the implementations described above referring to FIGS. 18 and19, in alternative four memory device implementations a memorycontroller can control addressing, replacing address multiplexors 2055,2065, 2067, and 2069, or can also replace switches 2020, 2030, and 2032.Similarly, in another implementation, a pair of memory controllers canbe used to replace pairs of address multiplexors 2055, 2065 and 2067,2069. These alternative implementations would have architecturesmodified from architecture 2000 in similar ways to how architecture 800can be modified to form architectures 1800 and 1900, as described abovereferring to FIGS. 8, 18, and 19.

FIG. 22 is a block diagram of one implementation of a switching dualpixel frame buffer architecture 2200 having four memory devices and amemory controller 2255 providing data and addresses to memories 2210,2215, 2217, and 2219. Memory controller 2255 replaces addressmultiplexors 2055, 2065, 2067, and 2069 in architecture 2000 of FIG. 20.

FIG. 23 is a block diagram of another implementation of a switching dualpixel frame buffer architecture 2300 having four memory devices and amemory controller 2355 providing data and addresses to memories 2310,2315, 2317, and 2319. Memory controller 2355 replaces addressmultiplexors 2055, 2065, 2067, and 2069, and switches 2020, 2030, and2032 in architecture 2000 of FIG. 20.

7. Checkerboard Buffer Using Alternating Sweeping

Returning to FIG. 7, in an alternative implementation, data destination715 is a GLV system that displays one column at a time, sweeping fromleft to right and right to left alternately with each frame projected.In this case, the address generation for retrieving pixel data frommemory used in the video destination or memory controller (such as videodestination 825 in FIG. 8, or memory controller 2355 in FIG. 23) ismodified. Based on the counter systems described above, when scanningleft to right in HD resolution, the column counter increments from 0 to1919 (or 0 to 959 if counting memory location columns rather than screencolumns). When scanning from right to left the column counters decrementfrom 1919 to 0 (or 959 to 0). The video destination uses the rowcounters in the same way as described above. The counter system of thevideo source for storing pixels is also unchanged.

8. Checkerboard Buffer Having Different Input and Output Data Rates

The rates at which pixels are stored and retrieved are different in someimplementations. For example, in one implementation, video source 805stores pixel data for 32-pixel blocks and video destination 825retrieves pixel data for 64-pixel blocks. In this case, videodestination 825 causes a frame to be displayed twice. Video destination825 retrieves pixel data for an entire frame in the same time that videosource 805 has provided half of the pixel data for a new frame. Videodestination 825 then retrieves pixel data for the same frame again whilevideo source 805 provides pixel data for the second half of the newframe. In one HD resolution implementation, the input pixel rate wouldbe 150 MP/S and the output pixel rate would be 300 MP/S, for a total of450 MP/S. Accordingly, a four memory device architecture, such asarchitecture 2000 in FIG. 20, can be used, such as with four 150 MHZ orfaster SDRAM's.

Various illustrative implementations of the present invention have beendescribed. The above description focuses on HD resolution video datadisplayed using a GLV system, but the methods and apparatus can beapplied to different resolutions and different devices. Similarly, thepixel data for a pixel is described above as being 32 bits, butdifferent depths are also possible with modification to the size of theaddressed memory locations. The present invention can be implemented inelectronic circuitry, computer hardware, software, or in combinations ofthem. For example, a checkerboard buffer can be implemented in variousways, such as with an FPGA, a hardwired design, a microprocessorarchitecture, or a combination. However, one of ordinary skill in theart will see that additional implementations are also possible andwithin the scope of the present invention. Accordingly, the presentinvention is not limited to only those implementations described above.

What is claimed is:
 1. A checkerboard buffer, comprising: a data source,providing data in a first order; a data destination, receiving data in asecond order; at least two memory devices, each memory device having aplurality of memory locations, where data is stored in parallel to thememory devices and retrieved in parallel from the memory devices, andwhere data is stored according to the first order using sequentialmemory locations in the memory devices; a first data switch connected tothe data source and each of the memory devices, where the first dataswitch controls which data is stored to which memory device; and asecond data switch connected to the data destination and each of thememory devices, where the second data switch controls providing data tothe data destination according to the second order; where: thecheckerboard buffer is a frame buffer for storing a frame of pixels, theframe having horizontal rows of pixels and vertical columns of pixels;the pixels are numbered from left to right, top to bottom, starting from0 in the upper left corner; the rows are numbered from top to bottom,starting from 0 at the top; the columns are numbered from left to right,starting from 0 at the left; the data is pixel data; each pixel in theframe has corresponding pixel data; pixel data for each pixel is storedin a respective memory location in a memory device; and pixel datastored in parallel is stored at the same address in each memory device;where a first destination address is provided to a first memory devicefor retrieving pixel data and a second destination address is providedto a second memory device for retrieving pixel data, and the firstdestination address is different from the second destination address. 2.The checkerboard buffer of claim 1, where the first destination addressis different from the second destination address by half of the numberof pixels in one row of pixels in the frame.
 3. The checkerboard bufferof claim 2, where the first destination address is different from thesecond destination address by
 960. 4. The checkerboard buffer of claim1, where the first destination address is always provided to the firstmemory device.
 5. The checkerboard buffer of claim 4, where the seconddestination address is alternately greater or less than the firstdestination address, alternating with retrieving pixel data for eachcolumn of pixels.
 6. The checkerboard buffer of claim 5, where the firstdestination address is different from the second destination address byhalf of the number of pixels in one row of pixels in the frame.
 7. Thecheckerboard buffer of claim 6, where the first destination address isdifferent from the second destination address by
 960. 8. Thecheckerboard buffer of claim 4, where a counter is used to generate thefirst destination address, and the counter is reset at the beginning ofretrieving pixel data for each column of pixels to half of the columnsprocessed plus alternately 0 or half of the number of pixels in one rowof pixels in the frame.
 9. The checkerboard buffer of claim 8, wherehalf of the number of pixels in one row in the frame is
 960. 10. Thecheckerboard buffer of claim 8, where the counter is reset at thebeginning of retrieving pixel data for each column to the sum of: (a)the quotient of dividing the number of columns processed by two, and (b)the 960 times the remainder of dividing the number of columns processedby two.
 11. The checkerboard buffer of claim 8, where which of 0 or halfthe number of pixels in one row in the frame is selected by usingwhichever was not used in the previous column, and where the firstcolumn uses
 0. 12. The checkerboard buffer of claim 1, where the firstdestination address and second destination address are providedalternately to the first memory device and the second memory device,alternating with retrieving pixel data for each column of pixels. 13.The checkerboard buffer of claim 12, where the first destination addressis reset to 0 at the beginning of retrieving pixel data for each columnof pixels.
 14. The checkerboard buffer of claim 12, where the seconddestination address is greater than the first destination address byhalf of the number of pixels in one row of pixels in the frame.
 15. Thecheckerboard buffer of claim 14, where the second destination address isgreater than the first destination address by
 960. 16. A checkerboardbuffer, comprising: a video source providing pixel data for pixels in aframe; a video destination; a first memory; a second memory; a firstdata bus connected to the first memory; a second data bus connected tothe second memory; a first address multiplexor connected to the firstmemory; a second address multiplexor connected to the second memory; asource address bus connected to the video source, the first addressmultiplexor, and the second address multiplexor; a first destinationaddress bus connected to the video destination and the first addressmultiplexor; a second destination address bus connected to the videodestination and the second address multiplexor; a first data switchconnected to the first data bus, the second data bus, and the videosource, where the first data switch is between the video source and thefirst memory and between the video source and the second memory, andwhere the first data switch switches which memory to store pixel datafor two pixels with each horizontal row of pixels; and a second dataswitch connected to the first data bus, the second data bus, and thevideo destination, where the second data switch is between the videodestination and the first memory and between the video destination andthe second memory, and where the second data switch switches the orderpixel data from each of the first memory and the second memory isprovided to the video destination with each vertical column of pixels;where pixel data is stored in the first memory and the second memoryaccording to horizontal rows of pixels in the frame, and pixel data isstored in sequential memory locations in the memory devices.
 17. Thecheckerboard buffer of claim 16, where each memory has a number ofmemory locations allocated for pixel data for half of each row ofpixels, and the number of memory locations allocated is half of thenumber of pixels in one row in the frame.
 18. The checkerboard buffer ofclaim 17, where the number of memory locations allocated is
 960. 19. Thecheckerboard buffer of claim 18, where a counter is used to generateaddresses.
 20. The checkerboard buffer of claim 19, where the counterincrements by 1920 after storing pixel data for a vertical pixel pair.21. The checkerboard buffer of claim 19, where the first data switchswitches based on the counter reaching a multiple of
 960. 22. Thecheckerboard buffer of claim 19, where the second data switch switchesbased on the counter exceeding 1,036,800.
 23. The checkerboard buffer ofclaim 16, where the video source generates source addresses for storingpixel data and the video destination generates destination addresses forretrieving pixel data.
 24. The checkerboard buffer of claim 16, where:each memory is divided into two memory sections, a first memory sectionfor storing data and a second memory section for retrieving data; ablock of data is stored to the first memory sections of the memorydevices and a block of data is retrieved from the second memory sectionsin alternation; and the memory sections switch roles between storing andretrieving with each frame of pixel data.
 25. The checkerboard buffer ofclaim 16, further comprising a memory controller that generatesaddresses for storing and retrieving pixel data, where the memorycontroller includes the first address multiplexor and the second addressmultiplexor.
 26. A method of storing pixel data in a checkerboardbuffer, comprised: storing pixel data for a first pair of pixels at afirst memory address in a first memory device and a second memory devicerespectively, where the first pair of pixels are the first two pixels ina first horizontal row of pixels in a frame; storing pixel data for asecond pair of pixels at a second memory address in the second memorydevice and the first memory device respectively, where the second pairof pixels are the first two pixels in a second horizontal row of pixelsin a frame and are vertically adjacent to the first pair of pixels;providing pixel data for a first pixel and a second pixel from a videosource to a data switch; providing a source address to the first memorydevice and the second memory device, where the source address is amemory address; controlling a state of the data switch, where in a firststate the data swithc provides pixel data for the first pixel to thefirst memory device and pixel data for the second pixel to the secondmemory device, and in a second state the data switch provides pixel datafor the first pixel to the second memory device and pixel data for thesecond pixel to the first memory device, and where the state switchesafter storing pixel data for each horizontal row of pixels; providingthe pixel data from the data switch to the first memory device and thesecond memory device according to the state of the data switch, andstoring the pixel data in the first memory device and the second memorydevice at the source address; where pixel data is stored in sequentialmemory locations in the memory devices.
 27. A method of retrieving pixeldata in a checkerboard buffer, comprising: retrieving pixel data for afirst pair of pixels from a first memory address in a first memorydevice and from a second memory address in a second memory devicerespectively, where the first pair of pixels are the first two pixels ina first vertical column of pixels in a frame; and retrieving pixel datafor a second pair of pixels from the first memory address in the secondmemory device and from the second memory address in the first memorydevice respectively, where the second pair of pixels are the first twopixels in a second vertical column of pixels in a frame and arehorizontally adjacent to the first pair of pixels; where pixel data isstored in sequential memory locations in the memory devices.
 28. Themethod of claim 26, where each memory device has a number of memorylocations allocated for pixel data for half of each row of pixels, andthe number of memory locations allocated is half of the number of pixelsin one row in the frame.
 29. The method of claim 27, where the number ofmemory locations allocated is
 960. 30. The method of claim 28, furthercomprising: generating addresses using a counter; and incrementing thecounter by 1920 after retrieving pixel data for a pixel pair.
 31. Themethod of claim 26, further comprising: generating a first destinationaddress and a second destination address, where each destination addressis a memory address; providing the first destination address to thefirst memory device; providing the second destination address to thesecond memory device; controlling a state of a data switch, where in afirst state the data switch provides pixel data from the first memorydevice to a first input of a data destination and pixel data from thesecond memory device to a second input of the data destination, and in asecond stare the data switch provides pixel data from the second memorydevice to the first input of the data destination and pixel data fromthe first memory device to the second input of the data destination, andwhere the state switches after retrieving pixel data for each verticalcolumn of pixels; providing pixel data from the first memory devicestored at the first destination address to the data switch; providingpixel data from the second memory device stored at the seconddestination address to the data switch; and providing pixel data fromthe data switch to the data destination according to the state of thedata switch.
 32. A method of storing pixel data and retrieving pixeldata in a checkerboard buffer, comprising: storing pixel data for afirst pixel and a second pixel at a first memory address in a firstmemory device and a second memory device respectively, where the firstpixel and the second pixel are the first two pixels in a firsthorizontal row of pixels in a frame; storing pixel data for a thirdpixel and a fourth pixel at a second memory address in the second memorydevice and the first memory device respectively, where the third pixeland the fourth pixel are the first two pixels in a second horizontal rowof pixels in a frame, and the third pixel and the fourth pixel arevertically adjacent to the first pixel and the second pixel,respectively; retrieving pixel data for the first pixel and the thirdpixel from the first memory address in the first memory device and fromthe second memory address in the second memory device respectively,where the first pixel and the third pixel are the first two pixels in afirst vertical column of pixels in a frame; and retrieving pixel datafor the second pixel and the fourth pixel from the first memory addressin the second memory device and from the second memory address in thefirst memory device respectively, where the second pixel and the fourthpixel are the first two pixels in a second vertical column of pixels ina frame and the second pixel and the fourth pixel are horizontallyadjacent to the first pixel and the third pixel, respectively; wherepixel data is stored in sequential memory locations in the memorydevices.
 33. The method of claim 31, further comprising: storing pixeldata for half of the pixels in a first row in a first block of memorylocations; storing pixel data for half of the pixels in a second row ina second block of memory locations; where each block of memory locationshas a number of memory locations equal to half of the number of pixelsin one row in the frame, and the last memory location in the first blockand the first memory location in the second block are sequential memorylocations.
 34. The method of claim 32, where each block of memorylocations has 960 memory locations.
 35. The method of claim 33, furthercomprising: generating addresses using a source counter; andincrementing the source counter by 1 after storing pixel data for apixel pair.
 36. The method of claim 33, further comprising: generatingaddresses using a destination counter; and incrementing the destinationcounter by 1920 after retrieving pixel data for a pixel pair.
 37. Themethod of claim 31, further comprising: providing pixel data from afirst output of a video source and a second output of a video source toa data switch; providing a source address to the first memory device andthe second memory device, where the source address is a memory address;controlling a state of the data switch, whore in a first state the dataswitch provides pixel data from the first output of the video source tothe first memory device and pixel data from the second output of thevideo source to the second memory device, and in a second state the dataswitch provides pixel data from the first output of the video source tothe second memory device and pixel data from the second output of thevideo source to the first memory device, and where the state switchesafter storing pixel data for each horizontal row of pixels; providingthe pixel data from the data switch to the first memory device and thesecond memory device according to the stare of the data switch; andstoring the pixel data in the first memory device and the second memorydevice at the source address.
 38. The method of claim 31, furthercomprising: generating a first destination address and a seconddestination address, where the destination address is a memory address;providing the first destination address to the first memory device;providing the second destination address to the second memory device;controlling a state of a data switch, where in a first state the dataswitch provides pixel data from the first memory device to a first inputof a data destination and pixel data from the second memory device to asecond input of the data destination, and in a second state the dataswitch provides pixel data from the second memory device to the firstinput of the data destination and pixel data from the first memorydevice to the second input of the data destination, and where the stateswitches after retrieving pixel data for each vertical column of pixels;providing pixel data from the first memory device stored at the firstdestination address to the data switch; providing pixel data from thesecond memory device stored at the second destination address to thedata switch; and providing pixel data from the data switch to the datadestination according to the state of the data switch.
 39. The method ofclaim 31, where: each memory device is divided into two memory sections,a first memory section for storing data and a second memory section forretrieving data; a block of data is stored to the first memory sectionsof the memory devices and a block of data is retrieved from the secondmemory sections in alternation; and the memory sections switch rolesbetween storing and retrieving with each frame of pixel data.
 40. Asystem for storing pixel data and retrieving pixel data in acheckerboard buffer, comprising: means for storing pixel data for afirst pixel and a second pixel at a first memory address in a firstmemory device and a second memory device respectively, where the firstpixel and the second pixel are the first two pixels in a firsthorizontal row of pixels in a frame; means for storing pixel data for athird pixel and a fourth pixel at a second memory address in the secondmemory device and the first memory device respectively, where the thirdpixel and the fourth pixel are the first two pixels in a secondhorizontal row of pixels in a frame, and the third pixel and the fourthpixel are vertically adjacent to the first pixel and the second pixel,respectively; means for retrieving pixel data for the first pixel andthe third pixel from the first memory address in the first memory deviceand from the second memory address in the second memory devicerespectively, where the first pixel and the third pixel are the firsttwo pixels in a first vertical column of pixels in a frame; and meansfor retrieving pixel data for the second pixel and the fourth pixel fromthe first memory address in the second memory device and from the secondmemory address in the first memory device respectively, where the secondpixel and the fourth pixel are the first two pixels in a second verticalcolumn of pixels in a frame and the second pixel and the fourth pixelare horizontally adjacent to the first pixel and the third pixel,respectively; where pixel data is stored in sequential memory locationsin the memory devices.
 41. A method of storing data and retrieving datain a checkerboard buffer, comprising: storing a first data element and asecond data element at a first memory address in a first memory deviceand a second memory device respectively; storing a third data elementand a fourth data element at a second memory address in the secondmemory device and the first memory device respectively; retrieving thefirst data element and the third data element from the first memoryaddress in the first memory device and from the second memory address inthe second memory device respectively; and retrieving the second dataelement and the fourth data element from the first memory address in thesecond memory device and from the second memory address in the firstmemory device respectively; where data is stored in sequential memorylocations in the memory devices.